Addition and subtraction within 20
Last year you added and took away numbers up to ten. Now we are stretching that — all the way to twenty. The idea is the same: plus means put together, minus means take away. Only the numbers are bigger.
Adding within 20
When you put two groups together, you add. The plus sign + means "and".
7 + 5 = 12
Seven balloons and five more balloons make twelve balloons. The total — 12 — is called the sum.
Subtracting within 20
When you take some away, you subtract. The minus sign − means "less".
14 − 6 = 8
Fourteen apples on the tree, six fall down — eight stay up. What is left — 8 — is called the difference.
Two kinds of problems
Inside this topic we look at two flavours:
- problems that stay below ten or jump cleanly to ten — these are easier,
- problems that "cross the ten" — like 8 + 5 or 13 − 7 — these are a little harder, but a great trick helps.
The trick: get to ten first, then go further. To do 8 + 5, take 2 from the 5 to make the 8 into 10, then add the rest: 10 + 3 = 13.
What you will learn here
- Adding to 20 — putting groups together
- Subtracting from 20 — taking away
- Worked examples — step-by-step solutions
- For parents — tips for grown-ups
When you are ready, try the exercise Addition & subtraction on the level "Up to 20" or build a tower in Pyramid.